This invention relates to invert oil emulsion well drilling and servicing fluids. In particular, the invention relates to invert oil emulsion well drilling and servicing fluids in which the internal aqueous phase contains a water soluble polyglycol dissolved therein, the fluids having good anti-settling properties as evidenced by an elevated low shear rate viscosity.
As is well known in the art, invert emulsion oil based well drilling and servicing fluids, generally called "muds", are water-in-oil emulsions that typically contain an organophilic clay viscosifier/suspension additive, and a weighting agent. The water phase is usually a solution of a salt, such as calcium chloride or sodium chloride, whose concentration is normally adjusted such that the aqueous activity of the fluid is equal to or less than the aqueous activity of the subterranean formations contacted by the fluids. This minimizes transfer of water to water-sensitive formations and maintains a stable wellbore.
The invert emulsion is usually stabilized with a "primary emulsifier", often a fatty acid or salt thereof, while the weighting material and the solids the fluid acquires during use are made oil-wet and dispersed in the fluid with a "secondary emulsifier", typically a strong wetting agent such as a polyamide, amido-amine (partial amide of a polyamine), and the like.
In recent years, environmental concerns over the effect of invert emulsion fluids on plant and animal life has led to the development of more environmentally-friendly fluids. Thus the oleaginous exterior phase of the fluids may be a so-called nontoxic and/or biodegradable hydrocarbon oil with low aromatic content, an ester, an ether, a synthetic hydrocarbon such as a polyalphaolefin, an internal olefin, and the like. However, the internal phase comprising aqueous solutions of calcium chloride and/or other halide salts are toxic to plant life.
Concern has been expressed by environmentalists and others with the possibility of polluting underground water supplies, damaging soil productivity and diminishing surface water quality. In a conference sponsored by the Environmental Protection Agency in May of 1975 in Houston, Tex., the effects of both techniques and chemicals used in drilling fluids and their impact on the environment were discussed. The outlook for landfill disposal of oil-base drilling fluids was not good. Such muds were thought to be toxic and the effects long-term. The toxic effect of oil-base muds on the soil was thought to be inherent in the chemicals used. Thus, known oil-base drilling fluids using a calcium chloride internal phase have adverse environmental consequences when used for land drilling operations.
Preferably, land farming could be used to dispose of both drilling fluids and the cuttings produced at a land drilling operation. And, the land farm would ideally be located near the site of the drilling operation. It should be appreciated that the cuttings contain an amount of drilling fluids. In land farming, the spent drilling fluids and cuttings would be spread over a section of land and plowed into the ground using standard agricultural methods. Drilling fluids using chloride solutions in their internal phases have proven too toxic to be acceptably disposed of by land farming, however.
Environmental regulations also restrict the concentration of halides, nitrates, sulfates and phosphates in drilling fluids used for land drilling operations. Thus, there is a need for oil-base drilling fluids having a composition that will comply with environmental regulations and will be environmentally compatible with land disposal methods.